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Once you know how and where to look, distinguishing a black gum tree (Nyssa sylvatica) from a live oak (Quercus spp.) becomes simple. Form, foliage, flowers and fruits all highlight the differences between these trees. Black gum simplifies the task when it drops its leaves for winter. A live oak -- as its name suggests -- stays evergreen. Southern live oak (Quercus virginiana) exemplifies the qualities that separate various kinds of live oaks from a black gum tree.

Silhouette and Size

Black gum's characteristic pyramidal shape remains intact throughout its life. Narrow but conical when young, the tree slowly widens as it ages. In Mediterranean-climate landscapes, black gum generally grows 30 to 50 feet tall and 20 to 30 feet wide. It grows much larger in its native eastern U.S. habitat yet still has a pyramidal form. Southern live oak grows 50 feet tall in Mediterranean climates and taller in its native southern U.S. realm; its rounded, umbrellalike canopy spreads twice as wide as the tree grows tall. A broad southern live oak on the horizon won't be mistaken for a black gum tree.

Leaf Characteristics

After a winter spent with bare branches, black gum produces glossy, green foliage in spring. Each broadly oval leaf widens in the center before its smooth margins form a point. Even in mild climates, black gum treats onlookers to a fiery show of red, orange, gold and purple foliage before fall takes its leaves. The southern live oak holds its leaves year-round in all but the coldest regions of its growing range, and there it drops only a portion of its leaves. The narrow, oval, smooth-edged leaves have softly rounded tips and are glossy and dark green on top and white underneath.

Preferred Conditions

Black gum and southern live oak grow best in full-sun and partially shady sites, and both tolerate highly acidic to highly alkaline soil pH. Hardy in U.S. Department of Agriculture plant hardiness zones 5 through 9, black gum withstands wide-ranging soil and moisture conditions. Compacted, drought-stricken, urban plots and overly wet, poorly drained sites both suit the versatile black gum. The tree has moderate salinity tolerance in a coastal location. Hardy in USDA zones 7 through 10, southern live oak adapts to a range of conditions, but its optimal growth requires consistently moist to wet soil. Even so, southern live oak excels in hot, inland climates and low-desert gardens that provide sufficient moisture. Its salinity tolerance is good to moderate on a coast and good at an inland site.

Flowers and Fruits

Some tree flowers have male and female parts within the same blossom, but black gum flowers are either male or female. With occasional exceptions, the male and female flowers occur on separate trees. After a male black gum tree's flowers pollinate a female black gum tree's inconspicuous spring blossoms, the female tree bears fruits, which appear in clusters and are black or blue-black, 1/2- to 1 1/2-inch, olivelike drupes in fall and winter. Southern live oak also has separate male and female blooms, but they appear on the same tree. Those blooms are insignificant and appear in spring; they yield 1/2- to 1 1/2-inch fruits -- brown acorns with spiny tips.

Other Live Oaks

While black gum blazes with fall color and berrylike fruits, live oak species native to Mediterranean, coastal climates stick with acorns and spiny, evergreen leaves. The coast live oak (Quercus agrifolia) is one of those species, and canyon live oak (Quercus chrysolepis) is another one. Hardy in USDA zones 9 through 10, the coast live oak grows up to 70 feet tall, has a canopy spread even wider and produces acorns measuring 1 1/2 to 3 inches. Every spring, it trades leathery old leaves for glossy new ones -- all with sharp, spiny edges. The canyon live oak is hardy in USDA zones 8 through 10, grows 65 feet tall and wide, and has sharp-tipped, 1/2- to 1 1/2-inch acorns. Its leaves may have sharp spines or be smooth; one tree can have both spiny leaves and smooth leaves. Each leaf is gray-green on top and pale-blue on its underside.

About the Author

Jolene Hansen is a lifelong gardening enthusiast and former horticulture professional. She is passionate about reshaping the way people experience gardens and gardening. Hansen's work appears regularly in consumer and trade publications, as well as numerous internet gardening and lifestyle channels.